The present invention relates to a photosensitive silicone-aromatic polyamide acid useful as a photoresist convertible to a patterned dielectric. More particularly, the present invention relates to a method for modifying a silicone-aromatic polyamide acid with nuclear bound acrylate amide groups which are introduced by effecting reaction between an acrylic organoisocyanate and silicone-polyamide acid.
Prior to the present invention, photoresists-like materials are described which are based on a photoreactive precursor, as shown by Rubner et al, Production of Highly Heat-Resistant Film Patterns from Photoreactive Polymeric Precursors, Part 1. General Principle, (January 1976) and Production of Highly Heat-Resistant Film Patterns from Photoreactive Polymeric Precursors, Part 2. Polyimide Film Patterns, (May 1976), Siemens Forsch.-u. Entwickl.-Ber. Bd. 5 (1976) No. 2, by Springer-Verlag. A photoreactive polyamide is made by initially effecting reaction between an aromatic dianhydride, for example, pyromellitic dianhydride and allyl alcohol. The resulting aromatic dicarboxylic acid diester is then converted to the corresponding aromatic diacid chloride by reaction with thionyl chloride which is further reacted with an aromatic diamine to produce a photoreactive aromatic polyamide ester. The aforementioned photoreactive polyimide precursor is then applied onto a substrate by spin coating and exposed with the aid of a mask, followed by developing the treated surface with an organic solvent to produce a negative photoresist. The negatively patterned aromatic polyamide ester is then heated to convert it to a patterned polyimide.
Although valuable results have been achieved with the aforementioned photoreactive aromatic polyamide ester, those skilled in the art know that the use of a chlorinating agent, such as thionyl chloride, to convert the aromatic dicarboxylic acid to the corresponding acid chloride prior to the polymerization reaction with aromatic diamine, can result in the generation of a residual chloride contaminant which can interfere with the utility of the resulting aromatic polyimide as a dielectric.
The present invention is based on my discovery that photosensitive polyamide acid useful as a photoresist and convertible to a patterned insulating layer free of chloride contamination, can be made by initially making a silicone-aromatic polyamide acid, consisting essentially of chemically combined units of the formulas, ##STR1## where R is a tetravalent C.sub.(6-30) aromatic radical selected from ##STR2## R.sup.1 is a divalent C.sub.(2-13) organic radical, R.sup.2 is a divalent C.sub.(2-8) organic radical, R.sup.3 is selected from C.sub.(1-13) monovalent hydrocarbon radicals and substituted C.sub.(1-13) monovalent hydrocarbon radicals, Q is a divalent radical having the formula, EQU --ZR.sup.4 Z--,
Z is selected from --O-- and --NH--, R.sup.4 and R.sup.5 are selected from C.sub.(2-18) organic radicals and n is an integer equal to 1 to 20 inclusive.
The above silicone-aromatic polyamide acid can be reacted with an isocyanato organo acrylate to produce a modified silicone-aromatic polyamide acid having chemically combined acrylate amide groups attached to the silicone-aromatic polyamide acid backbone by nitrogen-nuclear bound carbon linkages. Thereafter, a sensitizer can be added to the modified silicone-aromatic polyamide acid to produce a photoresist.